The RIP Protocol (Cont.)
When a router (or a host) receives such a broadcast, it adds all routes to networks it did not know about. For networks it already has routes to via a different router, it checks if routing via the new router will be "shorter" (smaller metric) then via its old route. If so, it updates its routing table.
In addition, each route is attached a 180 seconds timer, which is reset every time the route is re-received in a broadcast message. If the timer expires, the route is deleted from the routing table, assuming the router that advertised this route has failed (crashed).
To avoid routing loops from occurring when some router in the way fails, a "split horizon" method is often used - i.e. routes are not advertised back over the interface from which they were learned.